Today's mobile phones have various ways of notifying mobile phone users that someone called them but was unable to reach them. Three such prior art notification methods and their respective drawbacks are described below.
Notification Method:
    If a caller, A, calls a callee, B, but is unable to reach B then, in certain circumstances, A may leave a message on B's voice mail service.Drawbacks:    If B's voice mail is full then A is generally unable to leave a voice message.Caller A may not wish to leave a voice message.Notification Method:    If a caller, A, calls a callee, B, and is unable to reach B, then in certain circumstances B's mobile phone will record an identifier of the caller and the date & time of the call in a “Missed Calls” log.Drawbacks:    The Missed Calls log is only able to log calls that were made to B when B was located within a cell coverage area and B's mobile phone was turned on. Calls made to B when B was located in an area without cell coverage, or when B's mobile phone was turned off, are generally not recorded.If A has a blocked or an unlisted phone number, then A is not identified in B's Missed Calls log, making it impossible for B to return the call.If A has a listed un-blocked phone number, but B does not recognize it, then B may decide to discard the notification and not return the call.Notification Method:    If a caller, A, calls a callee, B, and is unable to reach B, then in certain circumstances, A's cellular service provider sends an SMS message to B's mobile phone with information about the missed call, including an identifier of the caller, and the date & time of the call.Drawbacks:    If A has a blocked or an unlisted phone number, then A is not identified in B's Missed Calls log, making it impossible for B to return the call.If A has a listed un-blocked phone number, but B does not recognize it, then B may decide to discard the notification and not return the call.
There is thus a need for alerting a callee, B, that a caller, A, called him but was unable to reach him, in a way that overcomes the above drawbacks, and without sacrificing A's security and B's privacy.